Suspension is probably one of the easier mods to DIY. You just need a little bit of common sense and some good tools.
I just upgraded to Bilsteins & Phat S-Techs last weekend...and my last four cars i also did my self (Holden, Ford, & BMW, etc)
Front = 2 - 4 hrs. Watch out for seized nuts and bolts, you are best off getting some second-hand replacements for a around $2.50 per unit from a Subaru wreckers before you start. (i had to cut/drill mine off as they were never ever ever going to come off without damage to the nut - even with a 1.8m breaker bar)
Rear = 1.5 hrs (including trim removal)
There's some walkthroughs somewhere on here or deep within the online matrix.
Basically if you can change a flat tyre with no hassles, you're half way there.

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Most important: Make sure someone/anyone/even a dog (called Lassie that can run for help if anything goes wrong) is there with you while you are working*(i will try and post a walkthrough up soon, with pics!!)
Good Luck!
Slow is the new fast... Not anymore!! Sort of...